linux-kernel - [PATCH v2 05/21] mm: list_lru: remove lru node locking from memcg_update_list_lru

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Message-Id: <20210527062148.9361-6-songmuchun@bytedance.com>
Date:   Thu, 27 May 2021 14:21:32 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     willy@...radead.org, akpm@...ux-foundation.org, hannes@...xchg.org,
        mhocko@...nel.org, vdavydov.dev@...il.com, shakeelb@...gle.com,
        guro@...com, shy828301@...il.com, alexs@...nel.org,
        richard.weiyang@...il.com, david@...morbit.com,
        trond.myklebust@...merspace.com, anna.schumaker@...app.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-nfs@...r.kernel.org,
        zhengqi.arch@...edance.com, duanxiongchun@...edance.com,
        fam.zheng@...edance.com, Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2 05/21] mm: list_lru: remove lru node locking from memcg_update_list_lru_node

Since commit e5bc3af7734f ("rcu: Consolidate PREEMPT and !PREEMPT
synchronize_rcu()"), the critical section of spinlock can serve
as RCU read-side critical section. So we can remove the locking
from memcg_update_list_lru_node().

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/list_lru.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 4962d48d4410..e86d4d055d3c 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -403,18 +403,9 @@ static int memcg_update_list_lru_node(struct list_lru_node *nlru,
 
 	memcpy(&new->lru, &old->lru, old_size * sizeof(void *));
 
-	/*
-	 * The locking below allows readers that hold nlru->lock avoid taking
-	 * rcu_read_lock (see list_lru_from_memcg_idx).
-	 *
-	 * Since list_lru_{add,del} may be called under an IRQ-safe lock,
-	 * we have to use IRQ-safe primitives here to avoid deadlock.
-	 */
-	spin_lock_irq(&nlru->lock);
 	rcu_assign_pointer(nlru->memcg_lrus, new);
-	spin_unlock_irq(&nlru->lock);
-
 	kvfree_rcu(old, rcu);
+
 	return 0;
 }
 
-- 
2.11.0